Immunogen is a commercial prebiotic. It is a natural compound such as beta golcan and mannan oligosaccharide that use as a feed complement. Usage of prebiotic as indigestible nutrient in digestion system that potentially affect health condition of host is a new idea for improving production in aquaculture. The aim of this study is survey bacteria flora and body composition of Barbus grypus in 360 pcs fingerling with 35±2 gr weight in 4 treatment group randomly. (3 replicates) treatments were feed by Immunogen with zero, 0/5, 1 and 1/5% respectively in 90 days. Result shows that Immunogen has positive effect on bacterial flora in fingerling. Lactobacillus population in intestine of treatment groups in contrast with control group (p<0/05). Results showed that the amount of carcass protein in 1.5% treated Immunogen was significantly higher than control (p <0/05) where as lipid content, ash and moisture showed no significant differences between treatments (p> 0/05), although this factor was slightly higher in group fed with 1.5% Immunogen. Therefore it can be concluded that oral administration of prebiotic Immunogen can induces positive effects on microflore of gut and Lactobacillus population plus carcass protein level.